1. Field of the Invention
The invention pertains to a brake system for a motor vehicle with an actuating device for the individual wheel brakes controlled by the brake pedal; the actuating device, which is connected to the brake pedal through electric lines and which causes brake linings to press against the respective brake disk, is an electromechanical wheel-brake actuator which is mounted on a mount for a brake caliper of the respective wheel brake. The system further includes a sensor disposed at the wheel brake which produces a signal that serves to control the wheel-brake actuator.
2. Description of the Related Art
In conventional motor vehicles, the braking force is controlled by the force exerted by the driver on the brake pedal. Braking interventions by anti-blocking or anti-lock devices, drive-stability control systems, drive-slip control or traction control and the like may be superimposed on this control. This is realized in conventional brake systems (see, for instance, German Patent DE-C 29 54 162) with hydraulic pumps and solenoid valves. In that case, however, the effect of the brake pressure on the braking operation cannot be accurately detected, since the brake-lining/brake-disk and tire/road coefficients of friction are not accurately known. The maximum braking force (adhesion limit) to be absorbed by a tire depends on the state of the tire and in particular on the state of the roadway; it varies within wide limits on a dry or wet roadway surface, in snow, on ice, etc. Since the maximum braking force is not known, the prior art anti-lock systems detect the adhesion limit via an evaluation of the wheel rotary speeds. The evaluation of the wheel rotary speeds and the determination of the adhesion limit is rather time-consuming.
In a published electromechanical vehicle brake (Automobil-technische Zeitschrift, 1996, No. 6, pp. 328-333), the driver's intention is passed via the brake pedal to a master computer which is responsible for the brake management of the entire vehicle. The master computer transmits the driver's intention to the individual brake modules, which set a required wheel braking torque for each individual wheel. Each wheel brake has a brushless electric motor which presses the brake lining against a brake disk via a spindle and is held on the caliper of the disk brake. A spindle nut is driven directly by the rotor of the electric motor. A rotary-position transducer (resolver) supplies an actual value for the engine governing and is used at the same time for the electrical commutation.
A prior art method of controlling the braking effect of hydraulically actuated brakes on aircraft landing wheels utilizes the wheel slip in order to control the braking force. The wheel slip is determined from the rotary speeds of a braked and an unbraked wheel (see German patent publication DE 12 60 324 B). The brake is released after a limit value of the slip is exceeded. In addition, the wheel load, as normal force, and the braking torque (brake moment) are measured, and then the wheel slip, the slip change per unit of time, the braking coefficient, the braking-coefficient change per unit of time, and the ratio of the braking-coefficient change to the slip change are calculated from the above-mentioned variables with the aid of an entire series of computers. The braking torque, which is detected with a torque sensor, enters with many other variables into a very complicated calculation of the ratio of the braking-coefficient change to the slip change, and it is this ratio alone which serves as the actual value for the brake control.
A prior art sensor for braking-force distribution systems and/or anti-lock systems for motor vehicles (German published patent application DE 19 27 282 A) detects the deceleration of the motor vehicle by measuring the stresses or extensions in a part stressed by deceleration forces, for example in the brake caliper of a disk brake or at the fixing point of the brake caliper, specifically with wire strain gauges attached there. Accurate measurement of the elastic extension enables the acting force and thus the deceleration to be deduced. The sensor produces an (actual-value) signal which is a measure of the deceleration of the motor vehicle.
A brake system for a motor vehicle of interest is described in a commonly owned copending application Ser. No. 08/899,748 (filed Jul. 24, 1997). That brake system has an actuating device for the individual wheel brakes which is controlled by the brake pedal via electric lines. The actuating device is designed as an electromechanical wheel-brake actuator which is mounted on the brake caliper of each wheel and by means of which the brake linings are pressed against the respective brake disk.